Outline Of Today’s Discussion
1. Dalton – The Color Challenged Monkey
2. Introduction to Color Perception
3. Color Metamers
4. Powerpoint’s Color Wheel
Part 1
Dalton:
The Color Challenged Monkey
Part 2
Introduction To Color Vision
Introduction To Color Vision
1.
Color is like “intelligence” in that it is one word which
describes a MULTI-DIMENSIONAL phenomenon.
2.
The three commonly studied dimensions of color are Hue,
Saturation, and Brightness.
3.
Let’s consider each of these in turn…
Introduction To Color Vision
1.
Perceptually, hue is the dimension of color that
distinguishes among red, orange, yellow, green, and blue,
as some examples.
2.
Physically, hue is the dimension of color most strongly
determined by light’s wavelength.
3.
Let’s look at the collection of wavelengths, ie., the
spectrum….
Introduction To Color
Intensity
Hue & Wavelength
Short
Green
Yellow
530
590
Wavelength (nm)
Long
Introduction To Color
Can someone show me where PINK is?
Introduction To Color Vision
1.
Perceptually, saturation is the dimension of color that
distinguishes pink from red, as one example.
2.
Physically, saturation is the dimension of color most
strongly determined by the extent to which a light is
LOCALIZED in the spectrum.
3.
A perfectly localized light would be “mono-chromatic”,
and would be a laser: It would be completely saturated.
4.
A completely “non-localized” (broadband) light would
appear achromatic. It would be completely de-saturated.
Saturation & Localization
Intensity
If this
is red…
Long
Short
Wavelength (nm)
Saturation & Localization
Intensity
Then this
is pink…
Long
Short
Wavelength (nm)
Introduction To Color Vision
1.
Perceptually, brightness is the dimension of color that
distinguishes “fire-engine-red” from maroon.
2.
Physically, brightness is the dimension of color that
distinguishes the amount of light emitted by an object.
Brightness & Intensity
Intensity
If this
is red…
Long
Short
Wavelength (nm)
Brightness & Intensity
Intensity
Then this
is maroon…
Long
Short
Wavelength (nm)
Introduction To Color
The Spectrum of Some Common Light Sources
Introduction To Color Vision
1.
What is color for?
2.
Color can be used to make objects conspicuous…
Introduction To Color
Color Makes Objects Conspicuous.
Isoluminant colors have the same intensity.
(Where’s the green shoulder-patch in right photo?)
Introduction To Color Vision
1.
Color can also be used to make objects inconspicuous,
that is, for camouflage…
Introduction To Color
Color Makes Objects Inconspicuous
Introduction To Color
Part 3
Color Metamers
Color Metamers
1.
Metamers are physically different stimuli that are
perceptually indistinguishable.
2.
Here are some color metamers. Name the colors you see
in the next slide…
Color Metamers
1.
Close one eye, and place the “red” (i.e., long wave pass)
filter in front of your other eye.
2.
Now, what color is seen in the center bar….
Color Metamers
1.
Finally, place the “blue” (i.e., short wave pass) filter in
front of your eye.
2.
Now, what color is seen in the center bar….
Color Metamers
1.
To the naked eye, the center bar always appeared yellow.
It did NOT appear to be “greenish-red”
2.
The filters reveal that the yellow experience was
composed of “green” and “red” light.
3.
Consider a canary yellow paper board. It’s spectral
composition would be a single, well localized spike, near
590 nm.
Spectrum of Yellow Paperboard
Intensity
You can’t
distinguish
this…..
Yellow
Short
590
Wavelength (nm)
Long
Spectrum of Center Bar in Demo
Intensity
from this!
Green
Short
Red
590
Wavelength (nm)
Long
Color Metamers
1.
That was an example of color metamers: Physically
different spectra gave rise to indistinguishable perceptual
experiences.
2.
Here’s another example of color metamers.
Color Metamers
Spectrum of RGB “White”
Intensity
You can’t
distinguish
this…..
Blue
Green
Red
Long
Short
Wavelength (nm)
Spectrum of Broadband “White”
Intensity
from this!
Broadband
Long
Short
Wavelength (nm)
Part 4
Demo:
PowerPoint’s Color Wheel
PowerPoint’s Color Wheel
1.
Using Powerpoint’s color wheel, let’s change some
background colors…quantitatively….
PowerPoint’s Color Wheel
1.
The International Commission of Illumination (Commission
Internationale de l’Eclairage, C.I.E.) has a 3-coordinate system for
describing color balances.
2.
The coordinates are decimals, respectively corresponding to Red,
Green, and Blue (RGB).
3.
The three “C.I.E. Coordinates” must always add to 1.
4.
So, we only need to specify the first two, and the third (blue) = 1 - (R +
G).
5.
Example: If R=0.4, and G=0.5, then B= 1-(0.4+0.5)=0.1.
6.
Let’s estimate the CIE coordinates for these stimuli….
Let’s make a good chocolate!
That is,
Using Powerpoint’s color wheel
to identify R,G,B values that
generate “a good Hershey’s Brown”